1. Field of the Invention
The invention relates to a fuel injector assembly having multiple control valves for controlling engine fuel injection rate and timing.
2. Background Art
Fuel injectors for internal combustion engines, particularly diesel engines, include an injector nozzle body for each power cylinder of the engine. A fuel injector nozzle in the nozzle body receives pressure pulses from an injector pump. In the case of a unit injector assembly, the pump body and the nozzle body are integrated into a common assembly. The pump includes a pumping chamber and a pump plunger in the chamber, the plunger being driven by an engine camshaft-driven cam and cam follower. The cam controls the injection rate and timing of fuel delivery to the nozzle of each engine combustion chamber.
German patent publication WO 02/31342 (A1) discloses a dual control valve arrangement for controlling distribution of fuel to an injector nozzle. The dual valve arrangement of the German publication is calibrated to take into account the necessity to increase vehicle exhaust gas emissions quality. It comprises a control valve system that will achieve optimum combustion efficiency with reduced undesirable exhaust gas emissions throughout each engine cycle. The valves are actuated by electromagnetic actuators, characterized by a minimum reaction time, to control signals distributed to the actuators by an electronic engine control, which monitors engine operating variables. This technique makes possible a rate shaping of a pressure time trace and a time trace for fuel injection rate to achieve minimum engine brake specific fuel consumption.
The valve assembly of the German publication includes a first valve actuated by an electromagnetic actuator between a closed position and an open position, together with an intermediate rate shaping position. The first valve, which is in communication with a pumping chamber, is effective to control the pressure distribution to the nozzle assembly by controlling the rate of fuel bypass flow or fuel spill past the valve to a low-pressure return circuit for a fuel supply pump. One of the valves of one of two embodiments described in the German publication normally is opened by a valve spring, and is moved to the closed position by an electromagnetic actuator comprising a first coil and stator assembly and a separate armature, the armature being connected to the valve. A second valve normally is biased by a valve spring to the open position and is actuated to the closed position by a second, separate solenoid actuator.
The outlet side of the second valve communicates with a nozzle needle valve, which creates a pressure force on the needle valve that complements the force of a needle valve spring. In this way, the shape of an injection rate time plot can be modified depending on the characteristics of the valve. The outlet side of the first valve communicates with a nozzle pressure feed passage to achieve a modified injection pressure that is controlled by its separate solenoid actuator.
Unlike the multiple valve assembly of the German publication with its separate solenoid actuator assemblies, the present invention comprises a single solenoid actuator that develops electromagnetic forces in proportion to known electromagnetic variables such as the core area, air gap between the stator core and the armature, material properties of the actuator and current level. The valve spring forces can be chosen to achieve the same or different effective forces for each valve, which makes it possible to calibrate and sequence the valve events depending upon current levels. The instant each valve is closed can be detected using a typical pressure transducer in accordance with one embodiment. In accordance with another embodiment, valve closure is detected by measuring a change in the inductance of solenoid actuator coils when armatures for the actuator stop moving.
The invention makes it possible to reduce the number of parts and to package the actuator in a compact injector assembly during manufacture.
The single solenoid driver for the valves reduces the manufacturing cost of the injector and reduces its complexity relative to known injector designs.
The actuator for the injector is under the control of an electronic control module for the engine. If the electronic control module is programmed to require exhaust gas recirculation control, this can be done readily by providing a sharp increase in the rate of pressure buildup for each injection rate for a given injection event rather than a more typical triangular-shape injection pressure buildup rate. By shaping the injection rate profile in this fashion in an injection rate time trace, undesirable particulates in the exhaust gas can be reduced. Furthermore, the shaping of the injection rate time trace will make it possible to improve the brake specific fuel consumption of the engine because it enables the engine to be operated with a more advanced injection timing.
In a typical engine, more exhaust gas recirculation will increase the percentage of the undesirable particulates in the exhaust gases. The particulates can be reduced by increasing mean injection pressure. This is made possible by delaying the beginning of an injection event through manipulation of the two valves.
In a first embodiment of the invention, an actuator armature drives an armature piston into a pressure chamber of reduced volume when the actuator stator is energized. This results in an increase in hydraulic pressure acting on each of the valves, which creates a pressure force that complements the effective spring force on each of the valves. The magnitude of the pressure in the pressure chamber is functionally related in a closed-loop feedback fashion to current in the actuator stator.
The timing of each of the valves can be calibrated using design parameters, such as spring rate, valve diameter, and actuator current.
When the single solenoid of the assembly of the invention is energized with a variable current controlled by an engine control module, the armature piston generates a pressure force that drives the valves. A closed-loop control of the pressure developed by the piston is effected using a pressure transducer. As the pressure generated by the piston increases, the sealing force of the valves increases.
The operation of the multiple valves can be sequenced by independently calibrating the valves. As each valve reaches its limit of travel during sequencing, a momentary pressure change will be detected by the pressure transducer.
In a second embodiment of the invention, the separate control valves are actuated by electromagnetic force rather than by hydraulic force. Each valve has a separate armature and a common solenoid assembly. Each armature is connected to its respective control valve. An inductance bridge circuit may be used to monitor the solenoid inductance to determine the timing of the valve movement using an electrical closed-loop control technique rather than a hydraulic pressure closed-loop control technique as in the first embodiment of the invention.
The stator of the second embodiment can be made with a single stator coil or a dual coil arrangement. In each instance, the solenoid assembly will create a valve actuating force level in proportion to known magnetic variables.